This results in body being visible (which is what I want), but it is click-through like the rest of the iframe. I want the body of the iframe to be clickable, but all the rest of the actual iframe element should be click-through.

The iframe is always bigger than the body inside of it.

Unfortunately I cannot access the the iframe content from the main site (so accessing the scrollHeight etc isn't possible), I can only change its actual source code.